As known, the perception of three-dimensionality can be obtained by reproducing two images, one for the viewer's right eye and the other for the viewer's left eye.
A stereoscopic video stream therefore transports information about two sequences of images, corresponding to the right and left perspectives of an object or a scene. Such a stream can also transport supplementary information.
International patent application PCT/IB2010/055918, published on 30 Jun. 2011 as WO2011/077343A1, describes a left/right image multiplexing method and a demultiplexing method (as well as related devices) which allow to preserve the balance between horizontal and vertical resolution, thus offering advantages over known techniques such as “side by side” and “top and bottom”.
According to said multiplexing method, the pixels of the first image (e.g., the left image) are entered into the composite image unchanged, whereas the second image is divided into regions whose pixels are arranged in free areas of the composite image, as shown in FIG. 1, which shows the case wherein two so-called 720p images are entered into a container frame 1080p.
In reception, the image divided into regions is reconstructed and then sent to the display. For examples, displays are known which operate in accordance with the so-called “frame alternate” principle, i.e., showing the two images L and R in temporal succession. For stereoscopic vision, so-called “active” glasses must be worn, i.e., glasses which, synchronized with the succession of images L and R, shade one lens and keep the lens of the other eye open, so that each eye can only see the image intended for it.
It is known that stereoscopic vision through such displays can prove annoying for some viewers, to whom it would be desirable to offer the possibility of varying (decreasing) the depth of the images so as to adapt it to their subjective preferences and to the size of the screen. To do so, it is necessary to provide, within the display, a synthesis of intermediate images between those being transmitted, which will then be displayed in the place of the actually transmitted images. Such a reconstruction can be done, by using known techniques, if one or more depth maps associated with the transmitted images are available.
Furthermore, so-called self-stereoscopic displays have recently begun to appear on the market, which do not require the use of glasses. Also such displays carry out a synthesis of non-transmitted images, and therefore require at least one depth map providing the information necessary for such synthesis.
It has thus become necessary to introduce a new format for generating, transporting and reconstructing stereoscopic streams, which format can be used for traditional 2D reception and reproduction devices and for current two-view stereoscopic 3D reception and reproduction devices (with or without depth adjustment), as well as for future self-stereoscopic devices using more than two views, while at the same time preserving the utmost compatibility of the format with the video stream production and distribution infrastructures and devices currently in use.